Apparatus and method of purifying water with ozone

ABSTRACT

An apparatus and a method for purifying a flow of water, by eliminating any Legionella bacteria present therein which comprises (a) means for providing ozone; (b) means for injecting the ozone into the flow of water, (c) a mixing chamber for mixing the ozone with the flow of water; (d) an outlet for the flow of water, and (e) electronic control means for the operation thereof: wherein the mixing chamber is of an inner geometry such as to create turbulence in the flow of water therein.

TECHNICAL FIELD

[0001] The present invention relates to the field of water purification.More specifically, it relates to the field of treatment of water in viewof eliminating therefrom any bacteria of the genus Legionella, inparticular of the species Legionella pneumophila, using an apparatus anda method wherein an ozone containing gas is utilised.

BACKGROUND OF THE INVENTION

[0002] The legionnaire's disease is caused by the pathogen Legionellapneumophila, which is a common microorganism in nature. Thelegionnaire's disease, as well as other diseases caused by Legionellabacteria, are severe conditions of epidemiological character which haveeven been known to cause death. More specifically, the bacteria willcolonize water supply systems, water heaters, showers, jacuzzi whirlpools etc. Severe problems have e.g. been observed in hospitals, inwhich cases the only solution has been to change the already colonizedpipings to all new equipment. Other fields where contamination byLegionella has been seen to cause problems are e.g. in the aerosol andrinse water of dentists and dental surgeons.

[0003] Temperatures of between 30-40° C. have been shown optimal for thegrowth of Legionella bacteria. In such an environment, a kind ofbiological film, or biofilm, comprising various bacteria andmicroorganisms, will appear. Some materials in pipes and packings aswell as where air pockets are formed, will enhance growth of theLegionella bacteria. In our modern society, in order to reduce costs,energy consumption often is lowered by decreasing the temperature of thehot tap water, whereby the growth of Legionella bacteria is in factencouraged, in turn resulting in an increased number of individualsafflicted with the diseases caused by Legionella. Accordingly, there isan increased need of methods which effectively control Legionellacolonization at reasonable costs.

[0004] Prior art methods of eliminating Legionella are byhyperchlorination, thermal treatment. UV radiation, by adding metal ionssuch as copper and silver ions. Of these, the simplest method has beenthe thermal treatment, i.e. heating the water to a temperaturesufficient to kill the Legionella bacteria present therein, a methodwhich however suffers from the drawback of increased energy costs andrisks of skin bums by hot tap water. On the other hand,hyperchlorination has the main disadvantage of corroding the waterpiping system and of possible production of carcinogenic by-products. UVtreatment may give rise to the formation of calcareous deposits on theUV source, reducing the efficiency of the treatment, and to a possibledamage of the lamps by contact with water. In the chemical watertreatment with metal ions there is an inherent risk of pollution of thewater by the chemicals added. Another proposed method is to kill thebacteria by use of 70% ethanol. The use of ethanol, however, gives riseto a fire risk. Moreover, the remedy obtained using these methods isonly temporary and with time the contamination problem is susceptible ofreappearing.

[0005] Ozone has been suggested in the prior art for the control ofvarious microorganisms. In nature, ozone is formed in the stratosphereand forms a layer protecting life on earth from deleterious UVradiation. Ozone as such is a strong oxidant and a toxic gas capable ofquickly and efficiently killing bacteria and virus. Accordingly,correctly used, ozone may be an advantageous disinfectant, even thoughcaution must be exercised to avoid harm on the environment and humanbeings.

[0006] It is known to use ozone in high concentrations for disinfectingwater from contamination by e.g. Legionella species. Indeed, U.S. Pat.No. 5,882,588 describes a process for continuously disinfecting hotwater using ozone. More specifically, said patent relates to the use ofheat transfer means to achieve hot water, of a temperature around 50° C.which under a reduced pressure is brought to a treatment tank.Meanwhile, an ozone containing gas, having a concentration of ozone ofpreferably 2-10%. is fed to the treatment tank from an ozonizer, whereinozone has been produced from oxygen. The pH is controlled in said tankby addition of HCl. In this patent it also is stated: “It can be learnedfrom scientific literature that a dose of 1-2 mg/l of ozone is expedientfor the treatment of tap water”.

[0007] In the preferred embodiment of the above cited U.S. Pat. No.5,882,588 the ozone containing gas is introduced into the hot water inthe reactor by passing it through a ceramic frit or analogousdistribution means, so that the ozone containing gas passes through thewater in the form of bubbles. Another patent, U.S. Pat. No. 6,001,247relates to an improved ozone dissolution system, wherein a sidestreamventuri injection system is combined with a specially, designed downflowtube. The advantageous effect provided by this patent is a decreasedrisk of the gas bubble channelling which may occur when higher ozoneconcentrations, such as 8-12% by weight, are combined with lower gasflows. The system according to this patent is however a complicatedapparatus comprising several diffusion chambers, reaction tanks etc,which requires a complex setting of tubing.

[0008] Application of ozone as a disinfectant also has been proposed inWO 981647, A2 (Long, Ron). This patent application relates to a point-ofuse filtration and ozonation drinking water treatment system andprocess. The amount of ozone to be injected into the water in order todisinfect it is not indicated. However a retained ozone residual ofbetween 0.1 and 0.4 parts per million in the disinfected water ismentioned, and it is stated that the ozone-containing water so producedmay be of use i.a. for rinsing surfaces, articles and food to reducemicrobiological contamination thereof.

[0009] Another patent application, EP 0315508 A1 (Kishioka, Takashi)relates to an ozonic bubble water generator which generates ozonicbubble water by mixing ozone into water. The ozonic bubble water isproposed for use e.g. as a disinfecting hand wash. Thus, as in WO9816473 A2. cited above, an outflow of ozonized water is proposed foruse as a disinfectant.

[0010] DK 166452 B1 (I. Krueger A/S) relates to a method of ground watertreatment wherein ozone is used to sterilise water which has been usedto rinse filters for the ground water. It is stated that at an ozoneconcentration of 0.01 mg/l, as much as 99.9% of the microorganismspresent in the rinse water are killed within 1 minute. The ozonetreatment of the water preferably is performed in a closed reaction tankand the treated water then is returned to the inlet for the non-treatedground water where any residual ozone in the treated water is used in anoxidation reaction of the incoming ground water.

[0011] From the above it appears that ozone has been used in variousapplications, including for treating water in order to eliminateLegionella therefrom. However, until now it has not been possible toeliminate, in a reliable, economical and simple way. Legionella from asystem of a flowing water and possibly water droplet aerosol, by use ofa very low ozone level and a very short treatment time, permitting toobtain a water outflow and water droplet aerosol which are alsoessentially free from ozone. This is the object of the presentinvention.

SUMMARY OF THE INVENTION

[0012] in contrast to the teachings of the prior art documents,according to the present invention elimination of essentially all ofLegionella bacteria present in a flow of water is obtained

[0013] at a much lower level of injected ozone, and

[0014] by a much shorter treatment time,

[0015] and this makes possible the treatment of the water flow by anapparatus located in close vicinity to the outlet for the flow of waterwithout any risk of outflowing water contaminated with harmful levels ofozone.

[0016] The location of the point of treatment in close vicinity to theoutlet results in the further advantage of reducing the risk ofre-contamination of the water with Legionella downstream of the point oftreatment, which re-contamination could occur in case the point oftreatment be located farther back upstream in the water supply system.

[0017] Consequently, according to the invention, by use of a level ofinjected ozone as low as 0.01-0.5 mg/liter of water, an essentiallytotal elimination, i.e. killing, of all Legionella bacteria present in aflow of water is obtainable within an extremely short time period oftreatment, such as less than one second.

[0018] Thus, in a first aspect, the present invention relates to anapparatus for purifying a flow of water, by eliminating any Legionellabacteria present therein which apparatus comprises

[0019] (a) means for providing ozone;

[0020] (b) means for injecting the ozone into the flow of water;

[0021] (c) a mixing chamber for mixing the ozone with the flow of water;

[0022] (d) an outlet for the flow of water, and

[0023] (e) electronic control means for the operation thereof;

[0024] wherein the mixing chamber is of an inner geometry such as tocreate turbulence in the flow of water therein.

[0025] Thus, according to an aspect of the invention an apparatus foreliminating Legionella present in a flow of water is provided.

[0026] Indeed, the mixing chamber is of an inner geometry geometry suchas to provide an essentially total elimination of any Legionellabacteria present in the flow of water entering the mixing chamber.

[0027] In a further aspect a method of obtaining a purified flow of isprovided, which method comprises the steps of

[0028] (a) providing ozone;

[0029] (b) injecting the ozone into a flow of water susceptible ofcontaining Legionella bacteria.

[0030] (c) mixing the ozone with the flow of water within a mixingchamber; and

[0031] (d) directing the flow of water to an outlet

[0032] wherein the mixing of the ozone with the water in step (d) isaccomplished by creating turbulence in the flow of the water within themixing chamber.

[0033] By the method of the invention a flow of water free fromLegionella bacteria is obtained. It thus is an advantageous aspect ofthe present method that an essentially total elimination of anyLegionella bacteria present in the flow of water entering the mixingchamber is achieved to provide a flow of water which is essentially freefrom any Legionella bacteria on exiting from the mixing chamber.

[0034] Thus, according to a very advantageous aspect the inventionpresent provides a simple, reliable and economical method of eliminatingLegionella from a flow of water, such as tepid water for taps orshowers, without any risk of a possible presence of any harmful residualtreatment chemical in the water delivered to the user, as well as anapparatus therefor.

[0035] It is a very advantageous aspect of the invention thatelimination of Legionella is achievable directly on-line in the flow ofwater essentially without any delay after actuating the valve regulatingthe outflow of water.

[0036] Aspects of the invention are further defined by the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]FIG. 1 is a bloc diagram representing one embodiment of anapparatus for disinfecting water according to the invention;

[0038]FIG. 2 is a schematic cross-sectional view of an embodiment of amixing chamber according to the invention;

[0039]FIG. 3 is a schematic cross-sectional view of another embodimentof a mixing chamber according to the invention;

[0040]FIG. 4 is a schematic cross-sectional view of an outlet for wateraccording to the invention;

[0041]FIG. 5 is a schematic cross-sectional view of an embodiment of aholding tank according to the invention; and

[0042]FIG. 6 is a schematic cross-sectional view of another embodimentof a holding tank according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0043] According to a first main aspect of the invention, an apparatusfor obtaining a flow of water which is essentially free from Legionellabacteria is provided. The apparatus of the invention basically comprisesa source of ozone, means for injecting the ozone into a flow of water, amixing chamber for ozone and the flow of water, an outlet for the flowof water, and optionally also an electrolytic chamber and filteringmeans preceding the outlet for the flow of water.

[0044] The source of ozone preferably comprises an ozone generatorgenerating ozone from the oxygen in a flow of an oxygen containing gas,to provide an outflow of an ozone containing gas. Most preferably itcomprises a means for collecting a flow of air from the surroundings andan ozone generator for generating ozone from the oxygen of the flow ofair, to provide an outflow of an ozone containing gas.

[0045] It should be understood that although the surrounding air is amost convenient source for obtaining ozone, the invention is by no meanslimited to this source. Also, the term “ozone containing gas” should beinterpreted to mean any appropriate gas containing the required level ofozone. It should also be construed to include the withdrawn aircontaining a required level of ozone after passage through the ozonegenerating means.

[0046] Preferably the source of ozone comprises means for drying and/oreliminating particles from the flow of gas, such as the flow of air,before it enters the ozone generator, e.g. a filter unit comprising amolecular sieve for eliminating humidity and a particle filter foreliminating particles.

[0047] The ozone generation per se is well known to those of skill inthis field and suitable means and measures are easily devised,optionally with reference to the literature within this field. In anadvantageous embodiment of the invention, a plasma resonance techniquemay be applied for generating an ozone containing gas from a flow ofoxygen containing gas, e.g. a flow of surrounding air withdrawn by meansof an air pump. As an example, an apparatus sold under the name ofOzonize by GRP Ltd. of Japan may be applied to this end, whereby ozonemay be produced at a rate of 0.05-1 g/hour at a gas flow of about0.4-2.0 l/min. Though the method of the invention is not limited to anyspecial technique for producing ozone, the produced ozone containing gasmost advantageously should be essentially free from nitrous oxides, socalled NO_(x). In the most advantageous embodiment, the means forgenerating an ozone containing gas has been set to provide an ozoneconcentration of from 0.1-2% by weight, more preferably 0.5-1% byweight.

[0048] Injection of ozone into the water flow is facilitated bygenerating a pressure drop in the flow at the point of injection of thegas, i.e. by a venturi effect. For example, by providing a device havingan inlet opening for the water flow and an outlet opening for the liquidflow, and having an inlet for the gaseous flow in a side-wall, andwherein the liquid inlet opening is substantially narrower than theliquid outlet opening, e.g. having a diameter which is 1.5-5 timessmaller, more preferably 2-3 times smaller, injection of the flow of gasinto the liquid flow is through the gas inlet is facilitated. As anexample, an inlet opening may have a width of 1-4 mm, more preferably1-3 mm and an outlet opening may have a width of 4-8 mm, more preferably5-6 mm. In general, a conventional venturi tube-shaped device, such asis described e.g. in McGraw-Hill Encyclopedia of Science & Technology,volume 14, pp. 346 (1977) will be appropriate. The gas flow inlet of thegas injection device preferably is preceded by a nonreturn valve orfunctionally equivalent means, to prevent backflow, e.g. into the ozonegenerator.

[0049] In a preferred embodiment, the venturi tube-shaped device is themixing chamber of the apparatus of the invention. The mixing chamber isa central part of the apparatus of the invention, in that it provides athorough mixing of ozone and water as well as an enhanced contactbetween the ozone and the Legionella bacteria possibly present in thewater flow, in a way enough efficient as to provide an essentially totalkilling of the Legionella bacteria within the time of flow from theinlet to the outlet of mixing chamber. This is accomplished by themixing chamber having an inner geometry which provides a turbulent flowtherein.

[0050] In one embodiment of a mixing chamber having such an innergeometry, the mixing chamber is equipped with at least two baffles,located at a distance from each other in the flow direction, andextending inwards in an essentially opposite direction to each otherfrom the inner walls and in an essentially perpendicular direction tothe water flow. Each baffle should extend over more than 50% or morethan 75%. preferably more than 90% or about 95% of the diameter of asection of the mixing chamber essentially perpendicular to the waterflow. For example, in a mixing chamber having an inner diameter of 20mm, a passage of 1-2 mm may be left open by the inwardly extendingbaffle.

[0051] In another embodiment of a mixing chamber according to theinvention, the mixing chamber comprises a restriction located at adistance from the inlet of the mixing chamber as well as the outlet ofthe mixing chamber, and an obstruction located at a small distancedownstream of this restriction. By forcing thus the flow of water andgas through the restriction and providing an obstacle on which the flowimpinges, turbulence and breaking up of possible bacterial colonies areenhanced. The restriction may be provided by two baffles, locateddirectly opposite to each other and extending inwards from the sidewalls over less than 50% of the diameter of the mixing chamber so as toleave a narrow slot open for the flow. Alternatively, it may be providedby one plate, integral with the walls of the mixing chamber and having asuitably shaped aperture for the flow of water.

[0052] Indeed, it is thought that by this turbulent flow, not only anefficient mixing of the ozone containing gas and the water susceptibleof containing Legionella is achieved, but also any colonies ofLegionella bacteria are efficiently broken down so as to expose eachbacterium and thus make it more accessible to oxidation by the ozone. Inthis way, and by use of the control means as will be described hereinbelow, elimination of Legionella in the water flow is obtainable on-linewithout any noticeable delay from the turning on of the water flow.

[0053] The invention thus allows for a very rapid eliminating ofessentially all of the Legionella bacteria entering the mixing chamberat a very low level of ozone. The water flowing out of the water outletwill consequently be free of any Legionella and also have no harmfullevel of residual ozone left, and more preferably has essentially noresidual ozone.

[0054] Generally, the mixing chamber will have a length of less than 100mm, preferably less than 70 mm or even less than 50 mm, e.g. from 25 to40 mm, and an inner width of less than 30 mm, preferably less than 25mm, e.g. from 18 to 22 mm. Obviously, the mixing chamber has a generallynarrow width, which also serves to enhance the contact of the ozone andthe water.

[0055] The term “inner”, as used herein in relation to the geometry ofthe mixing chamber, should be understood to refer to the geometry insidethe chamber, i.e. the shape of those parts of the chamber which face thelumen of the same, and which are susceptible of coming into contact withthe flowing water.

[0056] The material of the walls of mixing chamber 8 may any materialwhich is suitable for the intended use, e.g. withstands the pressure ofthe flow of water, and may be e.g. Teflon® or stainless steel. However,in case the walls of mixing chamber are made from a material which isdestructive to ozone, the inside of these walls should be coated with anappropriate material.

[0057] In one embodiment of the invention, surfaces inside the mixingchamber which are susceptible of contacting the water flow will becoated with a material which is both highly inert to ozone and resistantto fouling by microorganisms. Such a material may be selected from e.g.silicone, Teflon® and titanium dioxide. More preferably, this coatingwill cover the entire surface area within the mixing chamber susceptibleof coming into contact with the flow of water.

[0058] In another embodiment of the invention, surfaces inside themixing chamber which are susceptible of contacting the water flow willbe coated with a material which has a catalytic activity such asplatinum on activated carbon or on alumina, Pt/C or Pt/Al₂O₃.

[0059] Without wishing to be bound to any theory, it is generallythought that ozone may react directly with bacteria present in the flowof water or by the intermediate creation of hydroxyl radicals from thewater molecules of the flow, which radicals in turn may react with thebacteria present. An inert coating of the mixing chamber then wouldfavour reaction of ozone with water and bacteria, whereas a catalyticcoating would favour reaction of ozone with water. Both types ofcoatings thus would serve to further enhance the killing of bacteriapresent in the water flow.

[0060] In a further embodiment of the invention, the apparatus comprisesan electrolytic chamber. This chamber permits to regulate the pH of thewater flow to a desired value. The pH may be selected anywhere betweenapproximately pH 4 and 10, but it will be preferred to select a basicpH. i.e. higher than pH 7. Indeed, at alkaline pH values bacterialgrowth is inhibited. The basification of the water by means of passagethrough the electrolytic chamber thus may be foreseen as an auxiliaryprecautionary measure against the presence of Legionella bacteria in theflow of water. Electrolytic chambers are commercially available e.g.from DAE Medical of Korea.

[0061] Although the initial ozone concentration in the water is low, soas to eliminate any risk of harmful ozone levels in the outflowingwater, in one embodiment of the, a filtering means preceding the wateroutlet may be provided as an extra precautionary measure, whereby anyresidual ozone is eliminated from the outflowing water and whereinadditionally particles such as killed Legionella bacteria are retained.This filtering means preferably is a filter plate having a porousstructure such as a 30-60 mesh sieve and a small thickness, such as 1-5mm, more preferably 2-3 mm, so as not to give rise to an undue increaseof pressure within the water flow. It is comprised of a metal oxide,such as manganese dioxide. MnO₂, on a plate of activated carbon.

[0062] The functioning and power supply of the apparatus of theinvention is under the control of electronic control means, which maycomprise pre-programmed microchips to control parameters such as theparameters of the source of ozone, the water volume rate of flow, thetemperature of the water, the pH of the water etc.

[0063] In one specific embodiment of the invention, the means for mixingozone containing gas with water has been integrated in close vicinity tothe outlet for the water, such as in a shower mounting. The inventionalso relates to such an integrated unit as such, i.e. comprising meansfor mixing and an outlet, e.g. in the form of a shower handpiece, a tapetc. Such a unit is advantageous due to its great simplicity, enablinguse of already installed water supply systems simply by introducing thepresent unit. Accordingly, no expensive new investments are required,and there is no need to heat the water to high temperatures to preventcolonization of Legionella.

[0064] According to a further aspect, the present invention relates to aunit for eliminating Legionella from a flow of water, which comprisesthe apparatus described above fitted in a housing. In one embodiment,the present unit is a small, compact tin or box made from a corrosionresistant material, which is suitable for simple use in environmentswhere Legionella bacteria may be expected, or where the consequences ofany presence of such bacteria would be detrimental, such as inhospitals. The present unit is adapted to be connected to a tubing, e.g.made from silicone or Teflon®, which is fitted into the shower mountingor water outlet to provide mixing of outflowing water with ozone. As theunit never needs to contact the water, the electronics therein will beprotected from any damage and the system wherein the present unit isused will therefore also be safe for the user. By an appropriate fittingof the unit to the water outlet, elimination of Legionella will beaccomplished every, time the tap is switched on, thus operating in anisolated or non-continuous mode, contrary to the prior art continuousmethods.

[0065] The present apparatus of course will include arrangements oftubings, valves, pumps etc in appropriate materials for a reliableoperation. The skilled person in this field will without undue burdenset up such an apparatus with reference to his common general knowledgeof the field and the appended drawing and example. As for the electronicdevices and circuits required to control the present apparatus, such arebecoming more and more common in various chemical plants. It thereforewill be within the knowledge of the skilled person to choose theappropriate equipment, optionally after consultation of specialists inthe field of electronic control devices and process control.

[0066] According to another main aspect of the invention, a method ofobtaining a flow of water which is essentially free from Legionellabacteria is provided, which method basically comprises the steps ofproviding a source of ozone, injecting the ozone into a flow of water,mixing the injected ozone with the flow of water by creating turbulencetherein, and passing the flow of water to an outlet for water.

[0067] In an advantageous embodiment, the source of ozone is provided bycreating a flow of ozone containing gas. This may be accomplished bypassing a gaseous phase flow containing oxygen through a means forgenerating ozone. More preferably such gaseous phase simply is air.

[0068] Thus, in working a preferred embodiment of the present method,air from the surrounding room is collected into the apparatus viasuitable means, such as a pump. The quality of the air preferably isimproved by removal of undesired material, such as particles andhumidity, e.g. by use of a filter, wherein particles and humidity aretrapped. Said filter may be exchanged for any other suitable means,which means is easily selected by the skilled person in this technicalfield. The air is passed through a chamber or vessel, wherein ozone isproduced from the oxygen of the preferably dry air. Advantageously, theozone containing gas, comprised of ozone and air, is subjected to aslight overpressure, such as 0.01-0.3 bar, preferably 0.03-0.2 bar. Thisslight overpressure facilitates the subsequent injection of the gas flowinto the water flow.

[0069] Ozone suitably is injected into the water flow to reach a maximumlevel of ozone of about 0.01-0.5 mg/l. The electronic control meanscontrols the volume rate of flow of the gaseous phase which is injectedinto the flow of water to a suitable value in accordance with the volumeflow rate of the water flow, so that, having regard to the level ofozone in the gaseous phase, an appropriate flow of ozone is injected.

[0070] The flow rate of the water preferably is below 15 liters perminute or below 10 liters per minute and of course may be very low, suchas 1 liter/min and lower.

[0071] It is an advantageous aspect of the invention that thetemperature of the water flow to be treated is not critical. Indeed, itmay range between the temperature of cold and hot water, respectivelysuch as e.g. between 10 and 60° C. However, by use of the invention theneed of heating the water up to 60° C. in order to eliminate the risk ofcontamination by Legionella will be substantially avoided. Consequently,by applying the method and apparatus of the invention, it will bepossible to reduce the temperature of the hot water to any desiredtemperature, e.g. to between 38° C. and 50° C. depending on the hotwater requirements.

[0072] In one embodiment of the invention the water flow is passedthrough an electrolytic chamber wherein the water pH may be regulated toa desired value. For example, a pH between 4 and 10 may be set, asdesired. A basic pH, i.e. pH>7, more preferably pH>8. will result in aninhibition of any bacterial growth within the water flow. Theelectrolytic chamber thus may serve as an auxiliary means of providing awater outflow essentially free from any bacteria.

[0073] In another embodiment of the invention, the water flow issubjected to a filtering step to eliminate any residual ozone beforeexiting from the outlet. However, it should be noted that even withoutthis filtering step, any inadvertent residual ozone level in the wateroutflow will be negligible from a security point of view as it is atmost about 0.5 mg/l water in the mixing chamber, and may even usefullybe as low as at most 0.01 mg/l in the mixing chamber. If desired, asampling port, may be provided at an appropriate site in the system,e.g. directly upstream of the outlet for the flow of purified water.

[0074] In a further embodiment of the invention, where mixing chamber issituated within a flexible shower hose, the shower system comprisingthermostat, the flexible shower hose and mixing chamber is periodicallyflushed by injection of ozone therein. This is performed when the showeris not in use, under the control of the electronic control means.

[0075] It should be understood that in the light of the presentdisclosure the apparatus and method of the invention is applicable toany fluid system where a need for eliminating Legionella exists, byperforming the appropriate modifications. For example, the waterpurification apparatus and method of the invention could be applied foreliminating Legionella from the spray (aerosol) and rinse water ofdentists and dental surgeons. In this case the apparatus preferably willcomprise a holding tank downstream of the mixing chamber. This holdingtank preferably is made of a material such as stainless steel andequipped with an inlet for the purified water flow, a circulation loopproviding an outlet for the rinse and spray water by means of a pump anda valve as well as a draining outlet for emptying the tank. Furthermore,a gas exhaust is provided, e.g. comprising a pressure guard valve, whichsenses a rise in the internal gas pressure of holding tank and opens torestore normal pressure by venting off excess gas. The As a securitymeasure, pressure guard valve may be followed by a filter unit foreliminating any residual ozone in the gaseous flow.

[0076] In one embodiment the apparatus of the invention comprises aslightly modified version of the holding tank located downstream of themixing tank. This modified version of a holding tank will not compriseany circulation loop but simply an inlet for purified water and anoutlet for the same and preferably is connected to the water line bymeans of a shut-off valve.

[0077] The invention will now be further described by reference to theappended drawings. The drawings and the description should be construedas non-limiting examples of embodiments of the invention. Theyconsequently should be construed merely as an illustration of theinvention, and are by no means intended as a limitation to the scopethereof.

[0078] The cross sectional views, being only schematic, generallyrepresent the walls only as lines without any thickness, although ofcourse these walls should be understood to have a useful thickness, suchas e.g. to withstand a flow of water.

[0079]FIG. 1 schematically represents one embodiment of an apparatusaccording to the invention. This apparatus comprises a pump 1, forpumping air from the surroundings. The pump 1 is via tubing connected toa filter assembly 2, comprising a particle retaining filter and ahumidity absorbing molecular sieve. On the outlet side, filter assembly2 is connected to ozone generator 3. Ozone generator 3 is via nonreturnvalve 11 connected on the one hand to mixing chamber 8 and on the otherhand via magnetic valve 13 to thermostat 7.

[0080] Magnetic valve 12, followed by flow regulator 14, mixing chamber8 and magnetic valve 16 are located on the water line downstream ofthermostat 11. On the outlet side of magnetic valve 16 the line finallydebouches in the water outlet 10, here illustrated as a showermouthpiece.

[0081] On the gas line leading from the ozone generator 3 to the mixingchamber 8 a nonreturn valve 11 is located, to protect from any backflowof water into the ozone generator 3. An opening for injection of theozone containing gas is provided in a side wall at the inlet side ofmixing chamber 8.

[0082] The inner geometry of mixing chamber 8 is such as to facilitateinjection of the ozone containing gas flow through into the water flowand to provide thorough mixing of the ozone and the liquid phase as wellas breaking up of any bacterial colonies therein.

[0083]FIG. 2 represents one embodiment of mixing chamber 8, having aninlet opening 20 and an outlet opening 21 for the water flow as well asan inlet opening 22 for the gaseous ozone containing flow in a side wallin close vicinity to the inlet opening for the water flow. The inletopening 20 is narrower than the outlet opening 21. At a distance fromthe inlet side a first baffle 23 a is located, followed by a secondbaffle 23 b further downstream. The baffles 23 a, 23 b, both rigid andsolid (integral) with the inner wall, extend from a side wall in adirection substantially perpendicular to the flow of water and insubstantially opposite direction to each other. The diameter of inletopening 20 is 1-3 mm; the diameter of outlet opening 21 is 5-6 mm, thelength of the mixing chamber 8, as measured from the inlet opening 20 tothe outlet opening 21, is 25-35 mm and the inner diameter of mixingchamber is 20-22 mm. The baffles 23 a, 23 b, extending in oppositedirection each leave an opening passage for the flow of approximately1-2 mm.

[0084]FIG. 3 represents a further embodiment of mixing chamber 8, havingadditionally a restriction for the flow of water downstream of baffle 23a. This restriction is provided by means of a rigid plate 24, solid withthe inner walls of mixing chamber 8, having a small opening 25 for theflow of water. A curved baffle 26, located downstream of plate 24 andfacing the opening 25, provides an obstacle to the flow emerging throughopening 25. The curved baffle 26, with its convex side towards theopening, will provide an impact surface further enhancing turbulence anddisruption of bacterial colonies present in the water flow.

[0085] An electrolytic chamber 9 is connected to mixing chamber 8 via amagnetic valve 15, permitting to regulate the pH of the water flow at adesired value.

[0086] A shut-off valve 17 of the type with rotary ball (Ballofix®) isprovided to allow for manual sampling of the water flow downstream ofmixing chamber 8.

[0087] Within water outlet 10, here a shower mouthpiece, a filter plateis located, whereby any residual ozone is eliminated from the outflowingwater and wherein additionally particles such as killed Legionellabacteria are retained. In FIG. 4 the structure of an embodiment of sucha filter plate as well as its positioning within the water outlet 10 isschematically shown. This filter plate is of a porous structure such asa 30-60 mesh sieve, and has a thicknessof 2-3 mm. It is comprised of aporous plate of activated carbon 27 carrying a layer 28 of a metaloxide, such as manganese dioxide, MnO₂.

[0088] Finally, the apparatus comprises electronic control unit 4 toallow for the control of and power supply to pump 1, ozone generator 3and electrolytic chamber 9 as well as the control of magnetic valves 12,13, 15 and 16.

[0089] Additionally represented in FIG. 1, but not comprised in theapparatus per se, are cold and hot water pipings 5 and 6 and thermostat7, all conventional to any system for delivering thermostated water.

[0090]FIG. 5 schematically represents a holding tank 29 for use inassociation with the apparatus of the invention as applied foreliminating Legionella from a dentist's rinse or spray water. Holdingtank 29 preferably has a volume of 0.5-1 liter and is made of a materialsuch as stainless steel. It comprises an inlet 30 for the flow ofpurified water, a bottom draining valve 31 for emptying the tank ifnecessary, and a circulation loop 32 comprising a pump 33 and athree-way valve 34. A gas exhaust is provided by means of a pressureguard valve 35, which senses a rise in the internal gas pressure ofholding tank and opens to restore normal pressure by venting off excessgas. Pressure guard valve 35 is followed by a filter unit 36 comprisingactivated carbon.

[0091] In use, a flow of purified water from mixing chamber 8 entersholding tank 29 through inlet 30 until a preselected level is reachedwithin holding tank 29, whereupon the flow is disrupted. By the actionof pump 33, circulation of the water within the holding tank 29 andthrough the circulation loop 32 is obtained. By actuating the three-wayvalve 34, a flow of water may be withdrawn, to be used as a rinse orspray water.

[0092] In FIG. 6 holding tank 18 is represented, being a simplifiedversion of holding tank 29 as represented in FIG. 5. Holding tank 18 isthus comprises an inlet for water 30, connected by means of shut-offvalve 19 to the water line, i.e. the piping for the flow of water.Holding tank 18 furthermore comprises a siphon tube 37 and an outlet 38for water, outlet 38 being connected to to the water line whichdebouches in water outlet 10.

[0093] The functioning of the apparatus according to FIG. 1 will now bedescribed. By opening the magnetic valve 16 under the control ofelectronic control unit 4, water, such as a mixture of municipal coldand hot water entering through pipings 5 and 6 and mixed in thermostat 7to a suitable temperature, e.g. 25-38° C. starts flowing out of outlet10 at a flow rate regulated by flow meter 14. The control unit 4regulates the flow rate of the ozone containing gas in accordance withthe water flow rate. Air pump 1 simultaneously starts pumping in airfrom the surroundings into ozone generator 3, at a volume flow ratecontrolled by electronic control means 4. The quality of the air isimproved by removal of particles and humidity in filter 2, whereinparticles and humidity are trapped, whereafter the air flow enters ozonegenerator 3. In ozone generator 3, ozone is generated from oxygen of thedried air, which generation is controlled by control unit 4. The ozonecontaining gas flow exiting from ozone generator 3 is fed throughnonreturn valve 11 into mixing chamber 8 at a slight overpressure.Injection of the ozone containing gas into the flow of water withinmixing chamber 8 is obtained by a venturi effect. Within the mixingchamber 8 the flow of water and injected ozone containing gas is aturbulent flow, due to the special geometry of the mixing chamber 8.This turbulent flow will have the effect of decomposing the colonies ofLegionella susceptible of being vehicled by the water flow and ofproviding a thorough mixing of fluids and bacteria. The surfaces insidethe mixing chamber are coated either with a material inert towards ozoneor acting as a catalyst for the reaction of ozone and water molecules togenerate hydroxyl radicals to further enhance the killing of theLegionella bacteria. The water flow leaving mixing chamber 8 is fedthrough magnetic valve 16 under the control of control unit 4 andfinally flows out of water outlet 10, e.g. a shower mouthpiece.

[0094] Before leaving water outlet 10, the water flow is filteredthrough filter plate immediately preceding outlet 10, as a securitymeasure to remove any residual ozone in the flow by decomposing it tooxygen molecules.

[0095] Water flow leaving mixing chamber 8 is fed through magnetic valve15 into electrolytic chamber 9 and from there to outlet 10.

[0096] In the embodiment of the invention, where mixing chamber 8 issituated within a flexible shower hose, the shower system comprisingthermostat 7, the flexible shower hose and mixing chamber 8 isperiodically flushed by injection of ozone therein. This is performedwhen the shower is not in use, under the control of control unit 4. Forexample, at pre-programmed intervals of time, under the influence ofcontrol unit 4, pump 1 and ozone generator 3 start to work, magneticvalve 12 and 13 open and a short-time flushing of the system by ozonethrough valves 11, 13, 12, 16, flow regulator 14 and mixing chamber 8.

1. A method for purifying a flow of water in a water flow line by use ofan apparatus comprising (a) means for providing a flow of anozone-containing gas; (b) means for introducing the flow of theozone-containing gas into the flow of water; (c) a mixing chamber forturbulent mixing of the ozone-containing gas with the flow of water,located on the water flow line in the vicinity of (d) an outlet for theflow of water; and (e) electronic control means for the operationthereof; for providing a flow of water which on exiting through theoutlet for the water flow is essentially free from residual ozone andfrom contamination by Legionella bacteria characterised in that theozone-containing gas is introduced into the flow of water so as toprovide (i) a concentration of ozone in the water within the mixingchamber of at most 0.01-0.5 mg/l; and (ii) a contact time between theozone-containing gas and the water that is essentially equal to the timeof flow of the water flow from the water inlet of the mixing chamber tothe outlet for the water.
 2. A method according to claim 1 wherein themixing chamber (8) comprises at least two baffles.
 3. A method accordingto claim 2 wherein the baffles extend from the inner wall in a directionessentially opposite to each other and essentially perpendicular to theflow of water.
 4. A method according to any of claims 1-3 wherein themixing chamber (8) has the general form of a venturi tube.
 5. A methodaccording to any of claims 1-4, wherein surfaces inside of mixingchamber (8) that are susceptible of contact with the water flow are in amaterial that is essentially inert towards ozone.
 6. A method accordingto any of claims 1-5, wherein the surfaces inside of mixing chamber (8)that are susceptible of contact with the water flow are in a materialhaving a catalytic activity.
 7. A method according to any of claims 1-6,wherein the apparatus comprises a filter unit located downstream ofmixing chamber (8) and capable of eliminating any residual ozone and/orparticles such as killed Legionella bacteria from the water flow.
 8. Amethod according to claim 7, wherein the filter unit comprises a metaloxide, such a manganese dioxide, MnO₂, on a plate of activated carbon.9. A method according to any of claims 1-8, wherein an electrolyticchamber (9) permits to regulate the pH of the water flow to a desiredvalue.
 10. A method according to any of claims 1-9 in a tap, shower heador shower handpiece.
 11. A method according to any of claims 1-10,wherein the contact time between the ozone-containing gas and the flowof water is less than one second.